Research: Microbes are an option for ethanol, other biofuels

By Lisa Gibson

Microbes may be a big player in developing renewable fuels from cellulosic materials, and experiments are being conducted into how they can be used to convert sugars to ethanol and mixed-generation fuels. The topic was discussed at the recent meeting of the American Society for Microbiology.

Manufacturing ethanol from corn competes with food crops and has been accused of being responsible for rising food prices, according to the ASM. "The value of using nonfood crops is it will mitigate the significant food-versus-fuel debate," said Tim Donohue, professor of bacteriology at the University of Wisconsin-Madison, and director of the U.S. DOE's Great Lakes Bioenergy Research Center.

Researchers are looking at alternative biomass as feedstocks for microorganisms to ferment into ethanol, Donohue said. The most attractive is lignocellulosic biomass-wood residues, municipal paper waste, energy crops, or nonedible parts of corn such as cobs, stalks and stover.

"The same microbial activities used to generate ethanol from starch today can be used to generate ethanol and next-generation fuels from cellulosic feedstocks in the future," Donohue said.

The challenge is unlocking the sugars from the cellulosic biomass. Martin Keller, DOE Bioenergy Research Center director, and his team at Oak Ridge National Laboratory use an adapted method of high-throughput screening to rapidly test poplar tree samples for their ability to give up sugars. Some are more likely to release their sugars than others, which
Keller says could be because of genetics, environmental factors, or a combination of both. The team is growing poplar saplings in controlled environments to learn more, he said. They chose poplars because they grow quickly and in many different areas, Keller said, adding that his team also is experimenting with switchgrass.

Breaking down cellulosic biomass is an expensive process, but once that is overcome, several companies are ready to move forward with production, according to ASM.
Keller's team is also studying Anaerocellum, a bacterium found in a hot spring in Yellowstone. The bacterium grows at 80 degrees Celsius (176 degrees Fahrenheit) and can not only break down the cellulosic biomass to sugars, but it can also ferment it into acetate and ethanol, according to ASM. "This is called consolidated bioprocessing," Keller said. "This is only one strain that can do this, but none of the strains we have so far is perfect. You still need to optimize the strain. For instance, our strain is producing more acetate than ethanol."

Besides ethanol and biodiesel, researchers are also looking at producing hydrogen from renewable resources. Donohue and his lab are working with purple bacteria called Rhodobacter sphaerides that use photosynthesis to produce hydrogen. The hydrogen can then be converted to electricity using fuel cells the lab is developing. "On a laboratory scale, we can use sunlight and renewable waste to generate electricity in microbial reactors," Donohue said. Patents are pending, and he said the team does not have industrial-scale capacity for the project.

The most exciting part of current studies at the DOE energy research centers is the wide variety of disciplines represented by the researchers, Keller said, from molecular experts to chemists and engineers. "This has never existed before, bringing everyone together to target the problems we want to solve," he said "This will explode even more in the next couple years," he said.